1. Field of the Invention
The present invention relates to ionization devices for ionizing samples. Ionization devices described herein may be particularly useful in mass spectrometry imaging.
2. Description of Related Art
There exists a technique for ionizing a solid sample in an atmospheric pressure environment in order to analyze components in the surface of the solid sample.
In addition, research is being performed in the field of imaging mass spectrometry (IMS), in which, with the use of an ionization technique, an image that indicates the types of substances present on the surface of a sample and their locations on the surface is displayed.
Patrick J. Roach, et al., “Nanospray desorption electrospray ionization: an ambient method for liquid extraction surface sampling in mass spectrometry” Analyst, 135, pp. 2233-2236 (2010) and U.S. Pat. No. 7,910,881 each discuss a method in which a solvent is applied to a fine region of a solid surface in an atmospheric pressure environment and substances (solutes) that have dissolved in the solvent are ionized.
The method discussed by Patrick J. Roach, et al. uses two capillaries. The two capillaries are disposed such that ends of the respective capillaries are positioned in close proximity to each other. The solvent is supplied from one of the capillaries, and the other capillary transports the solvent that contains a solute from the solid (i.e., solution) to an ionization section.
A high voltage is applied to the solution in the ionization section, and thus the solute is ionized at the end of the other capillary.
The method discussed in U.S. Pat. No. 7,910,881, meanwhile, uses a capillary having a double-tube structure. The solvent is discharged to an end of the capillary from a portion between an outer tube and an inner tube. The inner tube is at a negative pressure and thus is capable of suck in the discharged solvent in which the solute has dissolved (i.e., solution). This capillary is brought close to the surface of the sample, and the surface of the sample is irradiated with laser light. Thus, desorbed substances can be dissolved in the liquid at the end of the capillary. The solution containing the solute moves through the inner tube and is introduced into a mass spectrometer.
According to the method discussed in Patrick J. Roach, et al., although ionization is carried out in an atmospheric pressure environment, only a substance that easily dissolves in the solvent can dissolve as a solute in the solvent, which leaves room for improvement. Meanwhile, according to the method discussed in U.S. Pat. No. 7,910,881, as the sample is irradiated with the laser light, a substance that does not easily dissolve in the solvent can dissolve in the solvent. However, since a process of taking a substance into the solvent (i.e., sampling process) and a process of causing ionization (i.e., ionization process) are carried out in separate locations, and a time lag exits between the sampling process and the ionization process. Thus, it is difficult to carry out the analysis at high speed.